build-sys: don't install sd-shutdown.h, it is a drop-in header like sd-readahead.h
update TODO
pam: the DECIMAL_STR_MAX macro is awesome, let's use it
util: add circle to special chars we can draw
socket-proxyd: no need to redefine sockaddr union
api: replace manual C++ guards by macros
shutdown: as sd-shutdown.h is a drop-in header it should not include any other headers of ours
activate: print a nice message if no fd to listen on was specified
socket-proxy: actually properly keep track of connections
bus: message_append_basic() - allow string == NULL